Homework Help:
Dynamic systems

I Have Just Received This Question = A Car Of Mass 1.2 Tonnes Rolls Down A Hill Which Is 600m Long And Is Inclined At An Angle Of 9 Degrees To The Horizontal. Ignoring The Effects Of Air Resistance And Friction And Assuming The Car To Start From Rest At The Top Of The Hill Calculate Its Speed As It Reaches The Bottom Of The Hill. I Think I Need To Calculate This Using A Vector But I Cant See How I Get The Speed. Please Can Some One Explain This As I Cannot Get My Head Around This Hope Some One Can Help Cheers Mark.

I Have Done Vectors But I Have No Examples With Another Object This Is What Is Puzzling Me And The Equation Which I Think Is Relevant V=s/t Please Help As I Dont No Where To Start Some Examples Would Be Great Thanks For Your Reply Mark.

please can i bother you again as i thought i would be able to answer the following questions after i got the speed here are the rest of the questions (b) calculate its acceleration down the hill (c) the time taken to reach the bottom of the hill (d) the change in the momentum of the car between the top of the hill and the bottom of the hill (e) the change in kinetic energy for the car between the top and bottom of the hill.
also if the brakes are applied at the bottom of the hill slowing the car at a rate of 7.5 m/s2 calculate the stopping distance andthe speed after 5 seconds of braking i am seriously lost as i dont know which equations to use as i have been looking in my notes and several text books and still havent got anywhere your help is much appreciated.

b) So you need an equation with Accel. (which you're trying to find), Distance (which you know), Vi and Vf (which you also know). What equation could you use?

c) Simple equation with Vi, Vf, a, and t.

d) Momentum is m*v, so what is it on the bottom compared to what it is on top (hint: on top, v = 0)

e) What is the KE on top? (hint: v = 0 again). And you already calculated the KE on the bottom of the ramp.

For the brakes, you can forget about the hill and just treat this as a 1D motion problem. You know the initial speed and you know the acceleration. You need an equation with Vf, Vi, a, and t again (which you used in part c) and don't forget that since you're braking, the acceleration is negative.

as for the momentum i calculated 1200 x 42.89 = 51.468 kgm/s but this does not give the change in momentum thanks for your help and quick reply as i am struggling as you can guess but will get there hopefully mark.